1. Field of the Invention
The present invention relates to a method of manufacturing aggregated particles.
2. Description of the Related Art
In an image forming apparatus according to an electrophotographic process, on an electrostatic latent image formed on a photoreceptor surface, charged toner is fed to develop the electrostatic latent image to form a toner image and the toner image is fixed on a recording medium to form an image. According to the electrophotographic process, when the toner is uniformly transferred on an electrostatic latent image, an image high in the image density and excellent in the image quality can be formed. When the toner is transferred and evenly attached on an electrostatic latent image, it is important that particle diameters of the toner particles are homogeneous to be narrow in particle size distribution width and charging properties are homogeneous. The particle diameter of the toner affects not only on the charging property but also on high definition reproduction of an original image. The toner having an appropriately small particle diameter, that is, toner having a particle diameter in the range of substantially 5 μm to 6 μm is effective in obtaining a high definition copy image. Accordingly, in order to homogenize and reduce the toner particle size, various studies have been conducted.
As a method of manufacturing a diameter-reduced toner, there has bee developed, for instance, a wet process that the toner is manufactured in an organic solvent or a mixed solvent of organic solvent and water. The toner manufactured through the wet process is referred to as a chemical toner. Among the wet process, an aggregation process has been known as a process of homogenizing toner particle diameters. According to the aggregation process, in aqueous slurry in which for instance fine resin particles, colorant particles and mold releaser particles are dispersed, an aggregating agent such as a divalent or trivalent metal salt is added to aggregate the resin particles, colorant particles and mold releaser particles to produce aggregated particles that are toner. In the aggregation process, a reaction vessel is used. The reaction vessel is a chamber-typed reactor onto whose outer circumference a heat-exchanging jacket is attached and inside of which a stirring blade is provided.
The aggregation process involves the following problems to be solved. The particles such as resin fine particles contained in the aqueous slurry are readily excessively aggregated, which results in formation of aggregated particles unnecessarily large in the particle diameter. Accordingly, as one of the problems, it is difficult to obtain at high accuracy aggregated particles which have desired particle distribution and shapes, and as another problem, it is required that an aggregation reaction be carried out over a long time to control particle diameters of aggregated particles. As still another problem, the colorant particles are irregularly exposed on aggregated particle surface to cause fluctuation in the charging property of individual aggregated particles and toner filming where the mold releaser particles are exposed on the aggregated particle surface and the mold releaser particles are melted and attached on a photoreceptor surface is caused, and thereby image defect is caused.
In view of such problems, a producing process of toner, in which, for instance, resin particles obtained by polymerizing polymerizable monomers in an aqueous medium in the presence of a surfactant having a polymerizing unsaturated group and a colorant are aggregated under heating and the presence of an aggregating agent is proposed (for instance, Japanese Unexamined Patent Publication JP-A 2003-345063). According to JP-A 2003-345063, a surfactant having a polymerizing unsaturated group is a nonionic surfactant having a polymerizing unsaturated group including a vinyl bond. As the aggregating agent, alkali metal salts, alkaline earth metal salts, salts of divalent metals such as manganese and copper and salts of trivalent metals such as iron and aluminum can be used.
The aggregating agent is dissolved in an appropriate solvent and added as a solution to a reaction system described in JP-A 2003-345063. Since when an aggregating agent solution is added, a reaction system of JP-A 2003-345063 is likely to cause the excessive aggregation, it is important to add the solution at a low aggregating agent concentration. For instance, in paragraphs [0132] through [0133] of JP-A 2003-345063, aqueous slurry containing 420.7 g of resin particles, 900 g of ion-exchanged water, 166 g of a colorant dispersion solution, 12.1 g of magnesium chloride hexahydrate and 1000 ml of ion-exchanged water is used. In the aqueous slurry, a concentration of magnesium chloride hexahydrate as an aggregating agent is only substantially 0.48% by weight. At such a low concentration, it takes a long time to aggregate. Furthermore, even when the aggregating agent is set at a low concentration, the excessive aggregation may occur; accordingly, it takes a long time to heat and agitate for temperature-up to an aggregation temperature and aging. Such a producing process is low in the productivity and cannot be carried out in an industrial scale. Furthermore, a problem is not solved that colorant particles are irregularly exposed on aggregated particle surface, resulting in fluctuation of the charging property. Still furthermore, numbers of the resin particles, colorant particles and mold releaser particles in individual aggregated particles are not uniform. Accordingly, a difference in component ratios among individual aggregated particles also results in fluctuation of the charging property.
Furthermore, a producing process of capsulated particles, in which, by use of a batch system, mother particles having a number average particle diameter in the range of 0.1 μm to 100 μm and daughter particles having a number average particle diameter one fifth or less the number average particle diameter of mother particles are processed with a homogenizer at injection pressure of 29.4 MPa (300 kgf/cm2) or more to aggregate daughter particles on a mother particle surface, is disclosed (for instance, JP-B 7-75666). Still furthermore, in a technology of JP-B 7-75666, in order to inhibit the excessive aggregation from occurring to obtain particles homogeneous in the particle diameter, pressure of 54.8 MPa or more is necessary. A homogenizer used in the technology of JP-B 7-75666 is, according to page 3, fifth column and 8 through 18 lines of JP-B 7-75666, a homogenizer in which pressurized dispersion elements are collided with each other (such as a micro-fluidizer) or a homogenizer in which pressurized dispersion elements are collided against an inner wall (such as a Manton Gaulin homogenizer). The homogenizers all do not have a coiled piping such as a homogenizer used in the invention; accordingly, the homogenizers can apply shearing force but cannot sufficiently apply centrifugal force. Furthermore, according to the technology of JP-B 7-75666, an aggregation operation is carried out under such high pressure as 29.4 MPa or more, in some cases, 54.8 MPa or more as described above. Accordingly, when the aggregation operation is carried out in an industrial scale, a pressure-proof apparatus and an escape apparatus are indispensable to necessarily result in a large scale homogenizer. That is, the process is not a practical one. Still furthermore, since only daughter particles having a number volume average particle diameter one fifth or less a volume average particle diameter of the mother particles can be used, usable daughter particles are restricted.
Further, there has been proposed a method of manufacturing a toner, in which method shape control of toner particles are carried out in a toner channel for the purpose of forming toners homogeneous in shape (for instance, Japanese Unexamined Patent Publication JP-A 2006-189710). According to JP-A 2006-189710, an aqueous medium containing resin particles flows through the toner channel under heat after aggregation of the resin particles or after fusion following the aggregation. The heating operation will generate surface tension which acts on the toner to be more spherical, thus forming the toners which are homogeneous in shape. As one example of the toner channel, there is stated a spirally-extending toner channel in JP-A 2006-189710. In the method of manufacturing a toner disclosed in JP-A 2006-189710, the aggregated particles flow through the toner channel after aggregation of the resin particles or after fusion following the aggregation, and it is therefore not possible to adjust the particle size of the aggregated particles although the shape thereof can be homogeneous. It is thus difficult to obtain at high accuracy the toner which exhibits an arrow particle distribution. Further, in the toner disclosed in JP-A 2006-189710, the resin particles are formed by a polymerization process, with the result that content and distribution of toner components such as a colorant in the toner particles are inhomogeneous, which causes the toner to be inhomogeneously charged.